In an attempt to minimize such pressure losses in elbows and bends it has been previously proposed to increase the transverse cross-sectional area of such elbows or bends at the radius of curvature. This, however, has resulted in an increase in turbulence in the fluid flow through such elbows or bends, and is self defeating in attempts to reduce pressure losses.
This is because an increase in radius at the extrados of the elbow or bend must be preceded and succeeded by a reduction in the radius of the extrados as it merges into the ends of the fitting. Thus, an attempted increase in the radius of the extrados in fact results in a reduction of the actual radius of the extrados, which in turn results in an increase in the skin friction and promotes the formation of eddy currents and separation effects in the downstream direction of fluid flow.
Typical in these respects is the disclosure to be found in White, U.S. Pat. No. 1,215,451, in which the radial extent of the extrados is increased, but, actual radius of curvature of the longitudinal axis of curvature remains unchanged.
Nordell U.S. Pat. No. 2,303,949 avoids this problem in White by arranging for the extrados to lie on the quadrant of a circle tangent to the pipe ends and parallel to the longitudinal axis, and, by an increase in the cross-sectional area of the elbow intermediate its ends by increasing the radius of curvature of the intrados. However, so doing results in the central longitudinal axis of the flow path being moved in a radially inward direction, i.e., it effects a decrease in the effective radius of the elbow with the disadvantages of increased turbulence and eddy currents in the fluid flow and an increase in the pressure losses.
This invention seeks to eliminate the disadvantage in White, by providing an extrados which is a quadrant of a circle tangent to the pipe ends, while at the same time eliminating the problem inherent in Nordell of movement of the central longitudinal axis of the elbow in a radially inward direction.
The present invention departs entirely from Nordell's teaching by causing the central longitudinal axis of the elbow to be positioned in a radially outward direction, thus providing an increase in the effective radius of the elbow, while at the same time providing for the formation of a compact elbow having a short center-to-end distance, in which the pressure drop is reduced to that of an elbow of considerably larger radius.